For example, PTL 1 discloses a conventional technique of arranging a multipolar ring magnet to each of both ends of a torsion bar, detecting, with magnetic sensor, a magnetic flux in accordance with a rotational displacement of a multipolar ring magnet, calculating a helix angle generated to the torsion bar based on the detected magnetic flux, and detecting a torque value from the helix angle. In this technique, to each of the multipolar ring magnets, two magnetic sensors having 90° phase difference of an electrical angle are provided, sin Δθ (square value addition value Z) relative to the helix angle is calculated based on outputs from total four magnetic sensors, and the torque value is detected based on sin Δθ.